In manufacturing electronic devices, plasma processing is performed to process a substrate. The plasma processing is performed by a plasma processing apparatus. The plasma processing apparatus generally includes a chamber main body, a stage, a first high frequency power supply, and a second high frequency power supply. The chamber main body defines an inner space as a chamber. The stage is provided in the chamber. The stage includes a lower electrode and an electrostatic chuck. The electrostatic chuck is provided on the lower electrode. The first high frequency power supply supplies a first high frequency power to generate plasma of a gas in the chamber. The second high frequency power supply supplies a second high frequency bias power to the lower electrode. A focus ring is provided on the stage to surround an edge of the substrate mounted on the electrostatic chuck. The focus ring is provided to allow ions to be incident on the substrate perpendicularly to the substrate.
The focus ring is consumed as the plasma processing time is increased. When the focus ring is consumed, a thickness of the focus ring is decreased. When the thickness of the focus ring is decreased, a shape of a sheath above the focus ring and an edge region of the substrate is changed. When the shape of the sheath is changed, a direction of ions incident on the edge region of the substrate is inclined with respect to a vertical direction. As a result, an opening formed at the edge region of the substrate is inclined with respect to a thickness direction of the substrate.
In order to form an opening extending in parallel to the thickness direction of the substrate in the edge region of the substrate, it is required to correct the inclination of the incident direction of ions to the edge region of the substrate by controlling the shape of the sheath above the focus ring and the edge region of the substrate. There has been developed a plasma processing apparatus configured to apply a negative DC voltage to the focus ring to control the shape of the sheath above the focus ring and the edge region of the substrate. Such a plasma processing apparatus is described in, e.g., Japanese Patent Application Publication No. 2008-227063.
In the plasma processing, supply and stop of supply of one or both of a first high frequency and a second high frequency may be alternately switched. In this plasma processing as well, it is required to correct the inclination of the incident direction of ions to the edge region of the substrate. Also, it is required to suppress electric discharge between the substrate and the focus ring.